1. Field of the Invention
The present invention relates to an organic light-emitting layer forming materials for an organic electroluminescence element (also called an organic EL element, hereinafter), an organic EL element, and organic EL display.
2. Description of the Related Art
Since a layer-type element in which a positive hole transporting organic thin film and electron transporting organic thin film were layered, was reported (C. W. Tang and S. A. VanSlyke, Applied Physics Letters, vol. 51, p. 913, 1987, for example), organic EL elements have been expected to be applied to flat panel displays as display elements having features such as self emission and high-speed response. They are a focus of particular interest as large-area light-emitting elements that emit light at a low voltage of not more than 10 V.
Fundamentally, a layered-type organic EL element has a structure of a positive electrode/positive hole transporting layer/organic light-emitting layer/electron transporting layer/negative electrode. Of these, the positive hole transporting layer or electron transporting layer can also play the role of an organic light-emitting layer, as in the case of the above-described two-layer type element of Tang and VanSlyke.
In order to obtain an organic EL element having a high luminous efficiency (that is, light emitting efficiency), it is necessary for the organic light-emitting layer to have a high luminous efficiency. For the constitution of the organic light-emitting layer, a pigment-doped film to which a small quantity of pigment molecules that emit strong fluorescence are doped as a guest into the major component in the capacity of a host material has been proposed, besides a single film formed from a single kind of material (for example, C. W. Tang, S. A. VanSlyke and C. H. Chen, Journal of Applied Physics, vol. 65, p. 3610, 1989).
However, the need for materials that have high luminous efficiency and are stable in a long duration of operation is not fully met by the present organic light-emitting layer forming materials for use in such applications.
As organic light-emitting layer forming materials, those having a polycyclic aromatic ring in the light-emitting molecular structure (for example, Japanese Unexamined Patent Application Publication No. 2002-124385 (claims)), and 1,3,6,8-tetraphenylpyrene derivatives (for example, Japanese Unexamined Patent Application Publication No. 2001-118682 (claims).) are known.